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Old 12-15-2008, 12:06 PM   #1
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Air Bag Suspension Installation

OK so for those of you that missed the thread "Pinion Angle? Whats A Pinion Angle?" I bought an air bag suspension system from a truck recycler. Its out of a 2007 Freightliner Semi. It seems everything is there in good shape. Here is a pic again,



It came with,
-two tanks
-two large arm spring type things with an air bag on the end of each
-a crossmember
-some pretty hefty brackets
-a valve of some sort

OK so the issue now is... well... um... how does this thing work??? I have a general idea of whats suppose to go on here but the valves are throwing me for a loop!? And why two tanks?

Elliot you seemed to know what you were talking about, or does anyone know of a place online that could offer some schematics or something that would explain how it all works. Everytime I search online I get answers like "Low rider air bags" or "bag your ride" commenting on little systems for cars and pick ups. It looks like the guys removing the system just snipped the hoses so I guess I need new hoses.

But whats this business with valves and leveling and jazz. I am in the middle of moving and its bloody freezing here so won't be working on it immediately but I would like to do it this winter yet. If all else fails maybe I will get a job at a heavy truck shop for a short time or something...
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Old 12-15-2008, 08:08 PM   #2
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Re: Air Bag Suspension Installation

I think they just threw in some junk they didn't need. I can't imagine you will need the crossmember or the 2nd tank. 2 tanks are a must for brake applications. The levelling valve is mounted in a "fixed position" and the air in your bags is controlled by it. Take a google on bendix. between them and goodyear they ought to have some useful info. If it would help I can take a pic of the levelling valve installed on my freightliner.
Just thought of it but if your bus has air brakes you wont need either tak...just plumb it into the existing tanks..keep your 2 put up somewhere in case your originals spring a leak.
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Old 12-15-2008, 10:19 PM   #3
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Re: Air Bag Suspension Installation

google
ridewell and hendrickson truck suspensions, IIRC they have installation and troubleshooting info for their airride setups
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Old 12-19-2008, 02:32 AM   #4
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Re: Air Bag Suspension Installation

Quote:
letz4wheel said
If it would help I can take a pic of the levelling valve installed on my freightliner.
Man if you would take a picture of the leveling valve that would be really helpful. My bus doesn't have air brakes so this system is literally starting from scratch. I don't need both tanks then? I noticed on one illustration I was emailed that there are two leveling valves. Do these just allow more pressure to be let into the bags as more weight is transfered to each side when cornering? I only see one valve with the set up they sold me!? And those hefty brackets have got to be for clamping the axle to the springs. My only other question is how I can make for absolutely positively sure that the rear axle gets installed perfectly parallel to the front axle? Do I just measure back from the front down the frame rails and mount the spring brackets in the same place or is this process more sophisticated than that?
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Old 12-20-2008, 02:56 AM   #5
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Re: Air Bag Suspension Installation

I have no idea how you are going to center the axle...I am a truck driver not a fabricator lol.
On my MCI the 2 levelling valves are on the rear axle. They allow each airbag on that axle to be controlled sepretly. On my steer axle it has only one valve it controls both bags...as it does also on the freightliner suspension.
Think of the levelling valve as a light switch. When it is "turned on" it is allowing air into the bags. When it is "turned off" nothing is happening. The only other thing it does is allows air out of the bags as more weight is added.
You could very well do the same thing manually with a plumbing ball valve, adding air to the bags untill you find the ride you like. The main problem with this solution is that if you have any air leaks you will have to readjust it in time.
The weather has been crappy in my part of the world. i do say though probably not as crappy as in your part. I will get some pics of the suspension when it clears up.
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Old 12-20-2008, 06:28 PM   #6
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Re: Air Bag Suspension Installation

To get the axle centered measure the wheelbase on both sides as a good starting point. Then also measure crosswise from a common point to a common point (left front spring hanger to right rear bracket for example) and make sure that measurement is square. You want to be pretty precise, but the truth of the matter is that being half an inch off with a wheelbase that long isn't going to case any noticeable crabbing. I don't think you'd even notice a pull in that case. FWIW when I do solid axle swaps or major suspension renovations on offroad rigs I shoot for 1/4" tolerance from side to side and it seems to work out ok.
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Old 12-20-2008, 07:42 PM   #7
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Re: Air Bag Suspension Installation



Uh-oh.

I can only give you some stray tidbits of general information. You probably need to spend some time googling for schematics and other info. Look for a big-rig mechanic's forum also, in case there is one.

And you could try the SchoolBusFleetMagazine forum -- they are "real" school bus people, but they have helped me with information on several occasions. Might be a big-rig mechanic among them. I suggest you invest some time making sure your inquiry there is very well written; thoroughly thought out, good syntax, correct grammar and spelling, so they don't blow you off as the kid they had to throw off their own bus yesterday. Use their "Garage" forum section.

But the best two sources would probably be the wrecking yard where you bought the parts, and a Freightliner dealer.

The wrecking yard ought to let you crawl under a similar truck with notepad and camera. You should also ask if they have a man who can explain it to you, but they may not have.

At the dealer, you should be able to just slide under a (nice clean!) new truck, again with notepad and camera. And they certainly will have knowledgeable people there. Now, since I don't know you, I'm going to tell you something that may or may not apply to you: When you go to the dealer, you should appear VERY mature and professional. If you and the dealership manager are standing next to each other, it should not be possible to guess which is which. I say this because big rig dealerships suffer under a steady flow of scraggly-haired cigarette-smoking buffoons who drive trucks, and you need to separate yourself from that bunch. You should appear to be a well-to-do grocery store manager who just might need to buy a small fleet of new Freightliners in another five years. Of course, I'm laying it on a bit heavy, but hopefully this makes sense.
Exactly how you proceed when you arrive, depends on the dealership. A large Freightliner dealer may have trucks on display on the front lawn that you can crawl all over on a Sunday morning without anybody ever knowing you are even there. At the other extreme, at a small shop somebody may shout "Hi, may I help you?" the moment you step out of your car.
Carry a clipboard with notepad, and a camera, and act with a purpose. No hands in pockets!
If you see a mechanic out in the yard, chat him up. If not, go in to the Service or Parts counter and chat that guy up, and show him big glossy photos of your bus project. Did I mention photos of your bus? Some roof raising photos will go a long way to establishing your credentials.

All right. Unless someone more knowledgable gives you detailed instructions for two valves, use one leveling valve. It goes on a crossmember near the axle. The valve has a lever, and the lever attaches to a rod that attaches to the axle. The length of this rod may be adjustable. There is probably a rubber bushing at each end, to allow movement. The valve should be in the middle of its travel when the suspension is in the middle of its travel. For correct suspension height, you will probably need Freightliner information. Then, you find the middle of the valve travel by lining up two small holes -- it's intended to stick a pin in it to hold it there while you adjust the rod.
The valve has a time delay feature so that no air moves when the suspension jumps up and down while driving. But when the valve moves to a new position for a longer time, such as when you load more cargo in the bus, then the valve changes the amount of air in the bags until the valve is level again. More weight = more air. Less weight = a hissing sound as air is let out.

(A (single axle) two-valve system would have one valve on each side, each controlling the bag on that side. This minimizes leaning in curves, methinks.)

The air suspension does not regulate your ride comfort. It controls the distance between the axle and the frame (on smooth ground). The leveling valve keeps this constant, no matter what. Ride comfort will change with the weight of bus and cargo, and the suspension does not know nor care. BUT... a lump of air is a much more compliant and sensitive spring than a slab of steel, and this is where you get your improved comfort. And the vehicle stays level in the bargain.

You will want to be certain that you install any additional valves that belong to the system, such as any that might regulate flow from side to side. I don't know what there might be, but you need to find out.

There is certain to be some adjustment in the suspension for aligning the axle in the chassis. It may be by shims, or by some sort of eccentrics, or both. Of course, you still need to install the brackets as accurately as possible, and only fine tune with the adjustments. My guess is, you can get very close by measuring from existing holes in the frame nearby, such as the old spring mounts.

As for crossmembers, you probably want to duplicate the Freightliner arrangement.

You shouldn't need more than one tank, except that two tanks in series is a good way to keep moisture out of the valves and bags.

If you can make friends with a big rig mechanic, you might consider hiring him for a weekend.

I don't know what else to suggest for now.
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Old 12-20-2008, 09:43 PM   #8
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Re: Air Bag Suspension Installation

lets try this again, ridewell manufactures airride suspensions for trucks and trailers, their website has "owners manuals" with thorough installation instructions, pictures and specifications for most of their products.

meritor and hendricson are also major suppliers of suspension systems.

with some luck, your new suspension might bolt up to the existing spring mount holes or at least you could use one of the existing holes in the frame to locate the front mounts for the rear suspension. the axle needs to stay in the same place relative to the frame (front to rear) so that the driveshaft splines don't bind or slip apart. their should be some sort of locating lug on the airride axle locating linkage, think spring centerbolt. the new crossmember has to be installed so that the airbags are vertical and have sufficient clearance to prevent the bags from rubbing on anything. the valves get mounted to the frame or crossmember and the linkage goes to the axle/suspension links, adjust the valve linkage to set your ride height somewhere in the mid travel point of the bags free height (fully colapsed and fully extended with no air/load on them) install both air tanks in series and plumb each valve/bag to the second tank to minimize moisture buildup in the system.

in your climate it would probably be advisable to install an automatic heated air drier to your air system, think bendix at the salvage yard when you go mshoping for your engine driven water cooled compresser with the brackets to intall on your engine.

spread the air ride parts out and take another picture so that we can see/tell more about the parts you have, I'm mostly interested in the mounts and heavy linkage pieces, the crossmember and air tanks are pretty much self explanitory.
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Old 12-23-2008, 01:13 AM   #9
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Re: Air Bag Suspension Installation

Quote:
Elliot Ness wrote,

Now, since I don't know you, I'm going to tell you something that may or may not apply to you: When you go to the dealer, you should appear VERY mature and professional. If you and the dealership manager are standing next to each other, it should not be possible to guess which is which. I say this because big rig dealerships suffer under a steady flow of scraggly-haired cigarette-smoking buffoons who drive trucks, and you need to separate yourself from that bunch. You should appear to be a well-to-do grocery store manager who just might need to buy a small fleet of new Freightliners in another five years.


Uh Oh! The dreads are another foot longer today.

I will take some more pics when I get a chance.
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Old 01-06-2009, 09:14 PM   #10
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Re: Air Bag Suspension Installation

Thanks for the encouragement...I think... Sorry for the delay was moving and didn't get the web till yesterday. Lots to catch up on I see. Hope everyone had a good holiday. Good to be back.
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